Hot metal spray guns



Dec. 4, 1956 l w. o. LEE ETAL 2,772,920

HOT METAL SPRAY GUNS Filed July 29, 1955 2 Sheets-Sheet 1 HEQ roeA/EXS DCC. 4, 1956 w. o. L EE ET AL HOT METAL SPRAY GUNS 2 Sheets-Sheet 2 Filed July 29, 1955 Y//// ///l` VV//A fl/ nitedSeates Patent 2,772,920 2 rMEfrAn .fsrnnwrcunss crims-priritympprieaaon .Grarn'rifin August 5,1954 i This inventionrrelatesonhotimetal?spraytguns of the kind in which a rod-orfwireof,metalrsrautomatically fed Vfrom a feed unit by means of a small driving motonand Y a'-reduetion=gear-into"arr"arc orilame'where th 'metal is melted and delivered through a nozzle in the form of a spray by means of a jet of compressed air or other gas. In such motors control of the density of the metal spray is effected by varying the feed rate of the wire into the gun, by varying the speedtof the driving motor.

Hot metal spray guns of this kind may be used to coat surfaces with thin layers of metal, and particularly in cases where the thin metal layer is to be used as an electrical surface heating element, for example as described in British Patent No. 703,374, it is desirable to be able to control accurately the density of the metal spray delivered by the gun in order to be able to control the density, thickness, and electrical resistance characteristics of the metal layer applied to the surface.

It is an object of the invention to provide means for controlling or indicating the rate of feed of the metal wire into the gun, since it is this feed rate which largely determines the density of the metal spray. The rate of feed is however relatively low and this creates difliculties in providing an accurate indication of the feed rate Without complex and expensive apparatus.

According to the present invention apparatus for indicating the rate of feed of wire to a hot metal spray gun of the kind referred to comprises a dynamo-electric generator arranged to be driven by the feed motor for the wire, and an electrical indicator device to which the output from-the generator is led and which thus provides an in dication of the rate of feed of wire.

It has been found that instead of using a frequency measuring instrument a simple current or voltage responsive device may be used as the indicator device with satisfactory results.

In any case the dynamo-electric generator is preferably driven directly by the motor, and thus at a relatively high speed in relation to the driving members of the wire feed unit. s

Preferably the dynamo-electric generator comprises a permanent magnet mounted for rotation between two or more pole pieces, the pole pieces being provided with a coil which is connected to the indicator device.

According to a preferred feature of the invention the apparatus includes a stroboscopic Calibrating or checking device, comprising a stroboscope disc connected for rotation with the motor, and means for illuminating at least part of the disc under intermittent light, the frequency of the intermission being controlled from a known standard frequency such as mains frequency.

In this case the apparatus will preferably include means for adjusting the setting of the indicator device to calibrate the indicator reading to the known rate of feed of the wire as determined from the known standard frequency.

2,772,920 PatentedvDeci 4, 1 956 ICC.

27.. `For.f,conveniencefthe stroboscope fdisc and/.therrotor of` thengeneratorrwill preferably ,be mountedwon' `the2motorE` shaftfitselff i Therrinventionamaylbe:performedwin rvarious-f differentey ways but one specific embodiment will nowfibe-'described by way of example, withreference to the accompanying electrical heating relerrent` on external aireraftf'surfacesy foiI iex'air'rpl'e as described and claimed in BritshTtent. 1510.701374. Hot metal spray gunsof. this. general. type are`"'wel1`kr'owri` andlin the# present. case' thergun includes.

shjwri) "whi'hf'are" Aarranged Lto, feedA a l1.5 of. sulst'a''iitiallyJ 4pure aluminium Athrough "a propane/oxygen ame, the molten metal being blown in the form of a spray through a nozzle 11 by compressed air admitted through a pipe 12. The propane and oxygen are supplied through conduits 13, 14. The density of the spray is controlled by regulating the speed of a motor 15 driving the feed unit 10 for thewire through a reduction gear 16,

and to control the amount of metal deposited on the surface an accurate indication of the rate of feed of the wire into the gun is needed.

The motor 15 comprises a variable speed 1/16 H. P. single phase electric motor linked to the feed Wheels of the unit 10 by the 150 to 1 reduction gear 16. The speed of the motor is controlled in known manner by a manual control yknob 17, while the current supply circuit 18 includes a master switch 19. The wire is fed to the propane/oxygen ame at the rate of 4.187 inches per turn of the feed wheels, and the speed of the wheels is variable from 3.5 to 16.5 R. P. M. The corresponding range of motor speeds is approximately 540 to 3580 R. P. M.

The apparatus for measuring the feed rate of the Wire comprises in general an alternating current electric generator connected to the feed motor of the gun and associated with an electrical indicator device. The generator comprises a rotor consisting of a small bar-type com- -pass magnet 20 and a stator in the form of a U-shaped laminated core 21 carrying a winding 22. The rotor 20 is mounted directly on the driving shaft 23 of the feed motor 15 and is arranged between the tips of the limbs of the stator core 21.

This generator has the desirable feature of imposing negligible torque load upon the wire feed motor 15, which is thus practically independent of the rate indicating system and unaffected by even a breakdown of same, yet gives an output substantially linear with speed over the normal operating range and sufficiently great to drive a suitably calibrated electrical indicating meter 24 (not shown in Figure 1 since it has been removed to show the generator). Due to the high output of the generator, and the substantially linear relationship between the speed of the rotor 20 and the mean current or voltage output of the stator windings 22, contrary to the usual practice of feeding a pulsating generator output into a type of frequency meter, in the present example the output of the generator is fed to a suitably calibrated volt meter or ammeter 24 through a full wave instrument rectifier 25 and a series resistance circuit 26, with an additional rectier connected in shunt with the indicating meter in order to improve the lineality of indication. In the present example the indicator device 24 is a moving coil microammeter of 200 ga. full scale deflection.

The indicator device thus constitutes a4 feed rate indicating device and may be calibrated by timing the feed period of measured lengths ofwire. ATo this end the apparatus also includes a stroboscopic checking device comprising a perforated strobe disc 27 attached to the main motor spindle 23 and a neon lamp 28 connected to mains A. C. supply 29 and specially adapted to glow only on the peaks of the supply voltage. The number of perforations in the strobe disc 27 may be calculated from the formula:

n=2f.60/ N where n.is the number of perforations in the disc 27. f is the mains supply frequency (c./s.) 29. N is the speedof the driving motor 15 in R. P. M.

i over* the apparatus is extremely light and compact, and

ismounted complete as one unit with the spray gun itself. What we claim as our invention and desire to secure by Letters Patent is: v

A hot metal spray gun comprising means for heating Y one end of a metal rod to a substantially molten state,

means for supplying a blast of gas adjacent said end of the metal rod to project the molten metal in the form of spray, and means for feeding the metal rod progressively towards the heating means including a motor, at least one feedwheel bearing on the rod, and a reduction gear interposed between the motor and the wheel, and means for indicating the rate of feed of the metal rod comprising a dynamoelectric generator driven directly by the feed motor at the same speed and an electrical indicator device comprising an electric motor selected from the class including voltmeters and ammeters to which the output from the generator is led.

Great Britain June 13, 1935 

